1. Field
Exemplary embodiments relate to light sources for display, and more particularly, to back light units for holographic display.
2. Description of the Related Art
A back light unit (BLU) for a holographic display uses highly coherent light when compared to a BLU for a liquid crystal display (LCD). The BLU for a holographic display is of a waveguide type. A diffraction grating is used to maintain coherency of light emitted from the waveguide. The diffraction grating may be manufactured as a surface corrugate type or a reflective index modulation type. A diffraction grating of a surface corrugate type or a reflective rate modulation type may be formed through a developing process and an etching process after exposing a coherent pattern that is formed by irradiating two laser rays on a photosensitive medium, such as a photoresist or a photopolymer. In terms of mass production, the surface corrugate type diffraction grating is widely used.
In a holographic display, a viewing zone for viewing a hologram may be determined according to a resolution of a spatial light modulator (SLM). When a currently commercialized LCD is applied to a holographic display, a hologram image may be viewed in a narrow region of, for example, a diameter of approximately 8 mm from a distance of approximately 1 m. Due to the region limitation, at least two viewing zones must be formed at locations that correspond to the eyes of a viewer, and the viewer may view the hologram image in a state of fixing the locations where the viewing zones are formed. In the case of a conventional BLU for providing a hologram image by using a holographic display of the related art, the structure is relatively complicated, and also, a relatively large number of parts is used to form the hologram image.